She said her son Christoffer had yoyoed between passive and hyperactive behavior until she had removed several staples from his diet including milk and grains.

Christoffer, today a normal 14-year- old, is one of 23 children suffering from hyperactive disorders who were put on milk-free diets in 1996-1997.

Their development has been tracked ever since by a small group of educators and researchers in the southwestern Norwegian town of Stavanger.

The group set out to prove a theory by Oslo-based scientist Karl Ludvig Reichelt that a metabolic disorder making it difficult to break down certain proteins, including casein (a protein in milk), could cause mental problems like Attention Deficit Hyperactivity Disorder (ADHD).

"One of the kids I worked with started on the diet on Wednesday and by the weekend his parents said they saw a huge positive change in his behavior," says special educator Magne Noedland, who helped spearhead the diet project.

All 23 children, aged between four and 11 years old when the project started, were suspected of having ADHD and had been shown to have abnormal levels of peptides in their urine.

The accumulation of peptides, short compounds containing two or more amino acids, is an indication the enzyme needed to fully break down and certain proteins is inhibited or missing, and can have an opium-like effect on the brain, according to Reichelt.

Many international research has been done linking such protein disorders to cases of autism and schizophrenia, and a growing number of studies also hint that some cases of ADHD are connected with the digestive problem.

There is however a lot of scepticism about the theory in medical circles, with many doctors believing medication like Ritalin is the best way to treat the condition.

Noedland acknowledges the Stavanger project does not meet all scientific standards, claiming the main problem is the lack of comprehensive studies on how many ADHD children suffer from peptide abnormalities.

"There is no reason to put every one with ADHD on a diet if only 10 percent of them have protein imbalances," he says.

The children in the Stavanger project all followed a strict casein-free diet the first year, and the results were overwhelmingly positive, Noedland says, pointing out that 22 of the 23 families reported clear improvements in their child's behavior and attention-span.

A number of the children have since stopped following the diet for different reasons and some were put on medication, but after eight years, six were still strictly avoiding all milk products and several had also cut out gluten, which is found in wheat, rye, barley and oats.

"We see a clear difference between those who stopped and those who stayed on the diet," Noedland says.

"Seeing these kids going from one day not being able to learn a thing to the next day being receptive; as a teacher that's a wonderful feeling," says Kristine Fosse, one of the educators involved in the project.

To illustrate her point, Fosse pulls out a writing test by a six-year-old boy who took part in the project.

The boy was asked to write his numbers after involuntarily breaking his diet and ingesting milk on September 22, 1996. The result was a confused and jumbled mess of squiggly lines. Just two days later, again strictly steering dear of casein, he repeated the exercise, this time writing four clearly legible numbers in an even line.

"It's incredible. We've seen intelligence tests that had gone steadily down suddenly turn around and go back up" after a change of diet, says Ann-Man Knivsberg, who covers the research end of the Stavanger project.

One of the children who still avoids. milk and gluten, 17-year-old Sigbjoern, says any lapse in his diet affects his performance in school.

"I can tell right away when I've eaten something I shouldn't. It's really hard to concentrate. I'm always careful before tests," he says, taking a big bite of gluten and milk-free carrot cake.

Considered a hyperactive problem child with retarded development in nursery school, Sigbjoern today ranks among the best students in his class.